/*
 * Copyright 2012-present Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License. You may obtain
 * a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package com.facebook.buck.rules;

import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;

import com.google.common.base.Preconditions;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DirArtifactCache implements ArtifactCache {
  private final static Logger logger = Logger.getLogger(DirArtifactCache.class.getName());

  private final File cacheDir;

  public DirArtifactCache(File cacheDir) throws IOException {
    this.cacheDir = Preconditions.checkNotNull(cacheDir);
    Files.createDirectories(cacheDir.toPath());
  }

  @Override
  public CacheResult fetch(RuleKey ruleKey, File output) {
    CacheResult success = CacheResult.MISS;
    File cacheEntry = new File(cacheDir, ruleKey.toString());
    if (cacheEntry.exists()) {
      try {
        Files.createDirectories(output.toPath().getParent());
        Files.copy(cacheEntry.toPath(), output.toPath(), REPLACE_EXISTING);
        success = CacheResult.DIR_HIT;
      } catch (IOException e) {
        logger.warning(String.format("Artifact fetch(%s, %s) error: %s",
            ruleKey,
            output.getPath(),
            e.getMessage()));
      }
    }
    logger.info(String.format("Artifact fetch(%s, %s) cache %s",
        ruleKey,
        output.getPath(),
        (success.isSuccess() ? "hit" : "miss")));
    return success;
  }

  @Override
  public void store(RuleKey ruleKey, File output) {
    File cacheEntry = new File(cacheDir, ruleKey.toString());
    Path tmpCacheEntry = null;
    try {
      // Write to a temporary file and move the file to its final location atomically to protect
      // against partial artifacts (whether due to buck interruption or filesystem failure) posing
      // as valid artifacts during subsequent buck runs.
      tmpCacheEntry = File.createTempFile(ruleKey.toString(), ".tmp", cacheDir).toPath();
      Files.copy(output.toPath(), tmpCacheEntry, REPLACE_EXISTING);
      Files.move(tmpCacheEntry, cacheEntry.toPath());
    } catch (IOException e) {
      logger.warning(String.format("Artifact store(%s, %s) error: %s",
          ruleKey,
          output.getPath(),
          e.getMessage()));
      if (tmpCacheEntry != null) {
        try {
          Files.deleteIfExists(tmpCacheEntry);
        } catch (IOException ignored) {
          // Unable to delete a temporary file. Nothing sane to do.
          logger.log(Level.INFO, "Unable to delete temp cache file", ignored);
        }
      }
    }
  }

  /** @return {@code true}: storing artifacts is always supported by this class. */
  @Override
  public boolean isStoreSupported() {
    return true;
  }
}